Last Updated on March 23, 2022 by Allison Price
Too much tension on the deepdigital flexor (DDF tendon) can cause a variety of problems in horse’s feet.
This includes differences in the appearance of front feet, clubbed feet and delamination on the hoof wall (whiteline disease).
The cause of excessive DDF tension in many cases is not known. There are many factors that could be responsible for excessive DDF tension, including developmental orthopedic disease (DOD), differences in the length of the thoracic and upper limbs, eating habits, etc. Standing with one leg forward and the other behind, pain in the affected limbs, standing with one leg forward and the other back, genetics and growth rate. The consequences of DDF tension increases are consistent, regardless of the cause.
One limb of the thoracic spine usually exhibits more DDF tension than another. The horse may have two front feet, one more contracted than the others. Our experience shows that the RF limb is more affected 70% of all the time.
Understanding the anatomy is essential to fully understand the impact excessive DDF tendon tension can have on the foot. From the deep digital muscle, the thoracic deep-digital flexor tendon is formed. Two parts of the DDF muscle attach to the ulna, and one (larger) attaches to the humerus. The muscle runs along the radius and eventually gives rise to the DDF tendon above the carpus (knee).
The DDF tendon runs behind the carpus, along the palmar aspect of the cannon bone, round the back of your fetlock and inserts under the third phalanx.
Two primary forces affect the foot structures: the DDF’s routing and attachments.
- Pressure across navicular bone.
- A downward- or rotational pull on the P3
1) A clubbed foot: The heel of a foot is considered “clubbed” when it has reached the point where it is breaking the distal leg axis forward. This is the area where the angle between the foot and the pastern is steeper. The tendon inserts are located on the underside P3. This will cause increased tension to pull the bone down, eventually leading to a high hoof angle and contracted heels. Malarticulation of the coffin joint or arthritis can result from a broken-forward axis. This can happen in either one or both of the front feet.
Realize that one foot might be smaller, more con-tracted, or higher than the other, but it does not necessarily mean that they are “clubbed”. However, a difference in foot angle does not necessarily mean that the “steeper limb” has greater DDF tension than its contralateral counterpart. Until the distal limb is moved forward (A), a foot isn’t considered “clubbed”.
2: Delamination/ “whiteline” foot disease.A downward rotation of P3 can cause separation of sensitive and insensitive tissue at the hoof’s laminar interface. This is known as delamination. This slow separation is not usually associated with pain or inflammation (laminitis). The separation/delamination is confirmed by the dissolution of the hoof wall.
Infusing a mixture of antibiotics, fungicides and astringents into the tissue can help to eliminate any infectious agents. This is how many owners deal with this problem. The primary problem isn’t infection, but rather, bacterial and fungi. Both bacteria and fungi exist all the time! Problem is that they have open spaces into which to infiltrate. The infection can be eliminated by closing the space.
3 Navicular inflammation: As it runs around the back side of the foot, the DDF tendon uses a fulcrum in the form of the navicular bone. This anatomy functions in the same way as a pulley to support a rope. An increase in tension on the DDF tendon can cause increased pressure to the navicular bone, which in turn causes inflammation. This is how horses get “navicular disease”.
4) Lamiitis:Laminitis can be caused by both biomechanical or metabolic processes in the laminae. Increased tension/ distraction at the laminar interface (via tension on DDF tendon), increases horse’s risk of developing laminitis. It also increases his/ her chance of suffering digital collapse (P3 rotation), once the tissue has weakened.
The DDF tendon tension can cause the above problems. Therefore, treatment strategies should be tailored to decrease DDF tension. Less DDF tension equals less pressure on the navicular bone, and less rotational pull upon P3.
Tension can be decreased by either lengthening or shortening tendon distances.
Young horses may benefit from treatment strategies that “stretch” or lengthen the DDF tendon, and/or limit the growth rate of associated bones. These are:
1) Trimming the heel as much as possible. This will increase DDF tension but also stretch t. It should not be done if the horse is lame or has evidence of hoof damage (dishing). This should not be done in older horses as it can worsen the problem.
2 Massage of DDF tendon muscles. This will decrease DDF tendon tension. A massage therapist is recommended to help relax the DDF muscles.
3) Decreasing energy intake. Some people believe that increased DDF tension is associated with a higher growth rate. Tendon tension can increase if the bones grow faster that the tendons.
4) A healthy diet. Flexural contracture (DDF tendon) is a sign of developmental orthopedic disorder (DOD). It has been linked to mineral imbalance (e.g. copper deficiency).
5 Distal accessory (check), desmotomy. This is an extension to the palmar ligament that runs backwards and joins the DDF tendon at mid-cannon bone. The distal accessory ligament prevents excessive movement of DDF tendon via its attachments. This helps to keep DDF tendon “check”. When excessive DDF tendon tension continues after the horse is 8-10 months old, distal accessory (check), desmotomy may be performed. The check ligament is cut to release tension and allow the DDF tendon to “lengthen”.
The DDF tendon loses most of its flexibility after 18-24 months. It is not able to stretch easily. Treatment strategies for older horses are often directed to reducing the distance between the tendon’s insertion and origin. Corrective shoeing is a common method.
Corrective shoeing and DDF tension reduction are two main ways DDF tension can be reduced.
However, there is a limit on how high one can raise the heels. Excessive heel elevation could lead to malarticulation of a coffin joint, crushing the heels, or excessive stress on the suspensory apparatus.
2 Facilitating foot breakover. By moving your foot’s breakover point backward (palmarad), you can reduce the stride length. This results in less limb/foot extension, and less tension on DDF tendon movement. You can move the breakover point backwards by trimming the toe, rolling the shoe or rockering it.
The farrier will grind or rasp the corner of the shoe when it is being rolled. This 90deg angle is eliminated, and the shoe is thus removed from the breakover. The farrier raises the shoe’s front off the ground when rockering it. This is usually around a 30deg angle. The farrier lifts the front corner of each shoe completely off the ground. This is not included in the breakover process. The shoe’s rocker can influence where the foot will split over. It is therefore important to understand the foot’s normal breakover patterns.
Farrier preference is usually the determining factor in facilitating breakover.
If excessive DDF tension (i.e. Transsection of the tendon might be an option in cases where excessive DDF tension (i.e. laminitis) is causing severe and/or life-threatening foot problems. The tendon can be cut to release its tension, which in turn dramatically reduces pressure on the navicular bone and the downward pull on third phalanx. This technique can be used to quickly and effectively relieve the clinical symptoms of excessive DDF tension. This technique is only used to salvage DDF tendon tissue. It is not intended for return to full performance.
The original cause of excessive DDF tendon may be unknown or not treatable, as we have already stated. DDF tension can continue to grow over time, putting pressure on our efforts to reduce it. There is no permanent treatment strategy that can be used to treat DDF tension.